Font size in the plugin

You need to add some custom CSS to your style.css in your theme:

To modify the whole rotator:
.testimonial_rotator { font-size: 1.1em; }

Just the title:
.testimonial_rotator_slide_title { font-size: 1.5em; }

Just the quote:
.testimonial_rotator_quote { font-size: 1.em; }

The Stars:
.testimonial_rotator_star { font-size: 48px; line-height: 48px; }

Depending on where your style.css loads on the page you may need to make a more exact selector. This just means you need more elements in the selector like:

body #content .testimonial_rotator { font-size: 1.1em; }

Can you post a link to your site? If not you may need the more exact selector:

div.testimonial_rotator_wrap div.testimonial_rotator { font-size: 1.1em; }